1. Technical Field
The present invention generally relates to measuring at least the density of a corrosive liquid by using at least two submerged corrosion resistant pressure sensors that are separated by a known vertical distance. The corrosive liquid may be erosive, abrasive, fouling, caustic, basic, acidic, capable of damaging sensors, or any possible combination thereof. In particular, the invention relates to an apparatus, system, and method for measuring the density of a corrosive liquid, such as drilling mud, by using at least two corrosion-resistant pressure sensors submerged in the corrosive liquid and separated by a known vertical distance to obtain at least two pressures at different depths in the corrosive liquid.
2. Background
With the discovery of new drilling techniques such as hydraulic fracturing, the United States is currently experiencing an energy bonanza. In addition to the wells being drilled with new techniques, many more wells are being drilled with tried and true techniques. All told, thousands of wells are being drilled every year in the United States alone. In every one of these wells, drilling fluids such as muds, cements or other slurries play an integral role in ensuring a safe and efficient drilling operation. For example, drilling mud is useful for controlling well formation pressures, removing well cuttings, and facilitating the cementing and completion of wells. Perhaps one of the most important functions of drilling muds is to help to prevent potentially devastating oil well blowouts. However, drilling muds are only effective at preventing blowouts when their properties, such as density, are properly adjusted. Real-time measurement of drilling properties is also used to help the rig operator understand down-hole conditions. Consequently, being able to measure the properties of these fluids while a well is being drilled is critical.
Up until now, traditional mud scales or balances have been used to measure the density (weight) of drilling fluid, cement, or any other type of liquid or slurry. Typically, the mud scales on a drilling site consist of a graduated beam with a bubble level, a weight slider along its length, and a cup with a lid on the end. The cup is used to hold a set amount of liquid to be weighed. The slider weight can be moved along the beam and a bubble indicates when the beam is level. Density is read at the point where the slider weight sits on the beam at level.
Mud scales are calibrated by using a liquid of known density (often water) and adjusting a counter weight. Generally, the scales are not pressurized, but a pressurized mud scale operates in the same manner.
A method for employing a traditional mud scale will now be described with reference to FIG. 1. First, mud is pooled, for example in a tank, in a pooling step 102. Second, a sample of the mud is collected in a known volume in a collection step 104. Third, the mud is weighed in a weighing step 106 to obtain the mass of the mud. Fourth, the mud's density is calculated in a calculation step 108 using the known volume and the mass of the mud. Fifth, the mud's density is reported to the drilling operator 110. This will permit the drilling operator to make adjustments to the mud's density if it is outside of a desirable density range and can provide useful information on down-hole conditions.
There has been no reliable, real-time method of determining the density of drilling mud. The old mud scale was the most reliable and simple way of making the determination, but it does not provide real-time data. For example, when drilling a well a mud sample typically will be drawn and density will be calculated once every hour for on-shore wells and once every 15 minutes for off-shore wells. Thus, if a mud density fluctuates soon after a sample is taken, it may be 20 minutes before a drilling operator realizes that the density fluctuation has occurred. This in turn may leave little time for implementing corrective measures to keep the mud density in a safe range or for taking other corrective measures to shut a well down. Accordingly, a device capable of measuring mud density in real-time is desirable for the additional safety, reliability, and efficiency it can provide.
Although some existing devices such as Coriolis and Venturi flowmeters can provide real-time density data, they have proven unreliable when operating under the corrosive, erosive, abrasive, fouling, caustic, basic, acidic or other harsh conditions imposed by drilling fluids. Drilling mud is typically made up of water, clay, and additives used to modify the mud's viscosity, density, pH and other properties. The mud creates an environment that is not conducive to prior art sensors. For example, the mud contains solids, including solids in the mud and well cuttings that can be abrasive or erosive. These solids can scrape a sensor and damage it. The mud also tends to be basic, which can damage a sensor by eating away at the sensor. Additionally, the mud can form layers on a surface that are difficult to remove. If the mud forms layers on the sensor, the sensor may become fouled and fail to work properly.
What is needed is a new and innovative device capable of autonomously transmitting real-time density data even under the harsh conditions involved in drilling. For example, a need exists for an apparatus that can measure the density of mud or other liquids every second of every minute during the drilling process and then transmit the measured data to provide operators with density data that is extremely accurate. Accordingly, the risks and liability associated with drilling wells could then be reduced while the reliability and efficiency of the drilling process is simultaneously increased. For example, there would no longer be a need to call out mud weight over intercoms. Instead, operators could receive real time read-outs of mud density and have peace of mind that a drilling fluid is operating within a safe density range.
It would also be beneficial if such apparatus were highly energy efficient, using for example, using only 24 watts of power. As a result, the embodiment can run off of back up battery power for long periods between charging by a solar charge. This is desirable for both environmental benefits and cost-savings.
It would also be beneficial if such apparatus were highly portable, comprising, a light-weight, compact unit. Such, a unit could be flown to remote locations by light aircraft or shipped at low costs due to its compact size and light weight. Furthermore, if the unit were constructed from weather-proof components and the mud probes were made from highly durable industrial materials, the unit would be capable of standing up to the rigorous conditions encountered at many drilling sites.